The invention relates to an airbag module.
From WO 96/25 309 an airbag module is known in which a diffuser is mounted above a gas generator and has a smaller cross-sectional surface area than the gas generator. The gas bag of the airbag module extends in the folded state mainly at the side of the diffuser and above the diffuser there is only one layer of the gas bag. The diffuser has outlet openings mainly at the side, i.e. in a direction extending transversely to the seat occupant.
The drawback with this arrangement is that the diffuser represents a source of danger for the occupant should he strike against the diffuser if the gas bag does not open or if the gas bag has already collapsed.
From EP 0 827 875 a steering wheel is known having a gas bag restraint system where the gas generator is mounted in a pot-shaped deformation element which lies with its base above the gas generator. Openings to allow the gases of the gas generator to flow out into the gas bag are provided in the base and at the sides of the deformation element. The deformation element thus likewise represents a diffuser. The gas bag extends in the folded state mainly at the side of this deformation element and only one layer of the gas bag lies above same.
The drawback with this arrangement is that owing to the outflow opening located in the base there is the tendency for the gas bag to unfold directly in the direction of the occupant which has a negative effect on an out of position occupant. Furthermore there is no stowage space available for the gas bag above the gas generator owing to the side wall of the deformation element being only slightly inclined there towards the axis of the gas generator. This is particularly disadvantageous in a steering wheel on account of the small space available for the airbag.
The patent specification EP 0 773 142 A1 describes an airbag module with a gas bag, a gas generator and a diffuser which encloses the gas generator and has a number of perforations over the entire diffuser body. The diffuser can hereby absorb the energy of an occupant striking against same. The drawback however is that the entire diffuser body is provided with perforations which represents an expensive solution. In addition the arrangement known from EP 0 773 142 A1 has the disadvantage that there is little stowage space for the folded gas bag and the gas bag unfolds immediately in the direction of the vehicle occupant during deployment.
The object of the invention is to design the airbag module so that it is formed at least in part in simple manner as a deformation element where stowage space for the folded gas bag is provided above the gas generator and where in the first phase the gas bag unfolds mainly transversely to the occupant.
According to this the diffuser or the housing has in the longitudinal section a stepped construction with a lower side wall area, an upper side wall area and a central side wall area connecting the upper and lower side wall areas. The diffuser or the housing extends in a lower side wall area at a distance from the gas generator and beyond the gas generator in the direction of the tear-open area of the module cover and thereby encloses at least approximately the same cross-sectional area as its section lying next to the gas generator. In this area the cross section of the diffuser or housing of the gas generator is thus larger than that of the gas generator. In an upper side wall area the diffuser or the housing of the gas generator has a smaller cross-section than the gas generator and in this area there are outflow openings for the gases of the gas generator to discharge into the gas bag transversely to the longitudinal axis of the diffuser. The lower and upper side wall areas are connected by at least one central deformable side wall area.
The arrangement according to the invention has the advantage that the section of the diffuser lying above the gas generator can as a result of its deformable central side wall area be shifted by the impact of an occupant away from same so that the risk of injury is reduced. Since the lower side wall area projects upwards beyond the gas generator the adjoining central side wall area also has sufficient room for the deformation in the direction of the gas generator. Owing to the smaller cross section of the diffuser or housing of the gas generator above the gas generator there is still sufficient space above same next to the diffuser or housing in which to store the folded gas bag. The utilization of the structural space available is thereby improved so that the targets set for reducing the geometry of the module can be easily met.
As a result of the openings in the diffuser or housing lying transversely to the longitudinal axis of the diffuser the gases enter into the gas bag crosswise relative to the occupant and a primarily lateral unfolding of the gas bag thus takes place. The gas flow is thereby first directed upwards in the lower side wall area and strikes the central side wall area. One part of the gas flow is diverted towards the outflow openings and the other part is eddied around in the space above the gas generator. The multiple deflection draws energy out from the overall system which has a positive effect on the thermal load on the gas bag fabric and the aggressiveness of the deployment of the gas bag.
The gas flow which is discharged from the outlet openings first forms in the upper module area a bubble from the fabric layer located above the diffuser fabric layer located above the diffuser or housing, with this process being made easier by the low package pressure existing in this area on account of the stepped structure of the diffuser. The bubble then expands laterally through the stepped release of the gas bag package from inside to outside until fully deployed.
Owing to the lateral unfolding the extension of the gas bag in the direction of the occupant is restricted to a minimum. The occupant is thereby not attacked in the normal position and the risk of injury to the occupant in an out of position area is minimized. No arrester straps or rip seams are required for the gas bag. Furthermore vibrations in the gas bag are reduced so that the gas bag occupies its optimum position for the protection of the occupant at an earlier moment.
The deformability of the central side wall area is preferably achieved by providing material weaknesses, more particularly in the forms of slits, in this area. These slits thereby have a width of at least approximately zero millimeters so that they primarily represent no outlet openings for the gases of the gas generator. In the case of a diffuser having a circular cross-section the slits preferably run radially.
It is expedient if the upper side wall area has a height which is less than half the height of the airbag module. Furthermore it is expedient if the upper edge of the diffuser or housing of the gas generator extends practically up to the module cover. The upper side wall area preferably has a cylindrical or conical shape.
The gas bag is preferably arranged around the diffuser and only one layer of the gas bag is located above the diffuser.
In one embodiment preliminary outlet openings are provided in the lower side wall area of the diffuser or housing of the gas generator to influence the pressure path. The preliminary outlet openings are preferably arranged so that they do not overlap with the outlet openings of the gas generator. They can be arranged for example above the outlet openings of the gas generator. The overall cross-sectional area of the preliminary outlet openings should be smaller than the overall cross-sectional area of the outlet openings of the gas generator. In one embodiment four preliminary outlet openings are provided.